Electric actuators have conventionally been used for various devices. For example, in the field of aircrafts, there is technical tendency of electrifying actuators in accordance with electrification of aircrafts. For example, electric actuators including a jack screw have been known. As another example, U.S. Pat. No. 4,578,993 discloses an electric actuator having a planetary gear mechanism, which is hereby incorporated by reference.
In an electric actuator having a jack screw, it is difficult to distinguish a sticking state (failure state), which may be caused by sticking of a foreign matter between a screw and a gear or seizure of a gear, from a state where an electric actuator cannot be extended due to equality between an external load and an output. Therefore, even if the electric actuator is normal, when the actuator is continuously unable to be extended due to an external load, the superior system may erroneously detect a failure of the electric actuator.
The electric actuator disclosed in U.S. Pat. No. 4,578,993 includes a set of planetary gears, another set of planetary gears, and a ball ramp detection device for detecting damage on the planetary gears. However, the ball ramp detection device disclosed in U.S. Pat. No. 4,578,993 cannot detect which of the multiple sets of planetary gears has been damaged.